Africa is the second largest region of the world ranked by population, after Asia. It occupies a land mass of 11, 447, 338 square miles. Its current population according to latest estimates by the United Nations is 1,349, 886, 357, making up 16.72% of the world’s population. Its population is young, with a median age of 19.7 years. 43.8% of Africa’s population is urban. Most of the world’s sickle cell disease (SCD) births occur in Africa. In light of these facts, no program or strategy to advance disease-modifying or curative therapies will have major or lasting impact without involving Africa or consideration from an African perspective.
Researchers using whole-genome sequencing data from 156 individuals with sickle cell trait (1 copy of the βs mutation Glu6Val, rs334) out of 2932 individuals from the 1000 Genomes Project, the African Genome Variation Project, and Qatar have posited that the initial βs mutation arose in Africa, possibly in the Green Sahara and Western Central Africa approximately 7300 years ago.1 The hemoglobin C mutation (β6Glu-Lys) is assumed to have arisen from a unique origin in West Africa (highest prevalence in Northern Ghana and Burkina Faso and rarely found in western Nigeria)2-5 and perhaps independently in Southeast Asia.6,7
Centuries before the first description of sickle cell disease (SCD) in the medical literature in 1910 by Dr. James Herrick in the United States, in Africa, SCD was recognized as a disorder that clustered in families, referred to by local dialects (referred to as chwechweechwe in Ga, nwiiwii in Fante, and ahotutuo in Twi), and was described with enough accuracy to permit tracing to several generations in a family in Ghana as early as 1670 AD.8 Evidence of SCD was found from studies of 6 predynastic Egyptian mummies dating back to 3200 BC.9
The βs mutation is an oft-cited example of balanced polymorphism where the heterozygous state confers a survival advantage over either homozygote. Studies in children from areas where malaria was hyperendemic show significantly less malarial parasitemia in those with sickle cell trait compared to those without it and demonstrated the similar distribution of sickle cell trait and hyperendemic malaria.10-12 Hemoglobin C trait and homozygous CC are also associated with a 29% and 93% risk reduction of clinical malaria, respectively.2,13
Historically, SCD was almost exclusively a disease of childhood, due to the high mortality rate, but with the early identification of individuals through screening programs (beginning in the mid-1970s), comprehensive care and disease-modifying therapies, as well as epidemiologic transition, a new chapter in the history of SCD is being written.
Environmental and Cultural Features Influencing SCD in Africa
The geographic distribution of the βs allele and therefore SCD within Africa is not homogenous and is influenced indirectly by factors such as altitude, rainfall, ...